Many semiconductor-manufacturing processes use hydrogen and/or ammonia gases. For example, the chemical vapor deposition (CVD) and the metalorganic chemical vapor deposition (MOCVD) processes employ hydrogen gas flow of about 30 to 100 standard liters per minute (SLPM). Silicon epitaxy processes also employ large hydrogen gas flow of above 50 SLPM. Gallium nitride manufacturing process typically uses ammonia flow of about 15 to 60 SLPM (50 to 150 SLPM for scale-up manufacturing processes), in addition to hydrogen flow of about 30 to 50 SLPM. Various metal nitrification processes require large flow of ammonia gas as the nitrogen source.
Since hydrogen gas is used either as a carrier gas or as a reducing agent in these processes, only a very small portion, if any, of the hydrogen gas introduced is actually consumed, and majority of such hydrogen gas is discharged with the process effluent gas stream. Such discharged hydrogen gas is either directly vented into the surrounding environment, or abated via combustion. Direct venting of the hydrogen gas can cause flames, or even explosions near the venting site, if the hydrogen concentration thereat reaches the flammability limit, which can be as low as 4% for hydrogen. The combustion of hydrogen gas, on the other hand, requires fuel and ignition equipments, and is therefore more costly than direct venting.
One object of the present invention therefore is to co-generate thermal and/or electrical energy during hydrogen abatement process, by deriving energy from the hydrogen gas, so as to reduce the overall energy consumption of the abatement process as well as the abatement costs. Hydrogen gas in the process effluent gas stream is therefore used as an energy source, which may provide energy to support the abatement process or other energy-consuming units of the semiconductor manufacturing facilities, or even being sold to the grid to as a revenue-generating commodity.
The conventional ammonia abatement methods use either wet scrubbing or combustions techniques. During wet scrubbing, the ammonia gas is scrubbed by an acid solution (e.g., HCl) to form a stable ammonia compound, such as ammonia chloride, and then discharged into the environment. The disadvantages of such wet scrubbing method include: (1) a large amount of water is consumed for scrubbing/dissolving the ammonia gas, and (2) the acid solution used during wet scrubbing itself constitutes contamination. The combustion method, on the other hand, converts the ammonia gas into water and nitrogen gas via combustion. The disadvantages of such combustion method include: (1) fuel and thermal energy are required for combusting the ammonia, which renders such method costly, and (2) NOx, which is a pollutant to the environment, is produced as a byproduct during the combustion.
Another object of the present invention therefore is to provide a method for co-generate thermal and/or electrical energy during ammonia abatement process, by deriving energy from the ammonia gas, and without incurring the above-described disadvantages of the conventional ammonia abatement methods.
Furthermore, certain volatile organic solvents contained in the semiconductor manufacturing process effluent gas stream, such as isopropanol, can also be abated using the method of the present invention, where the abatement and energy generation are concurrently carried out.
A further object of the present invention is to provide a self-sufficient system for effluent abatement and energy generation, while a part of the energy generated by such system is used to support the operation of such system, so that such operation is less dependent on fossil fuels. Moreover, the excess energy produced by such system can be returned to the manufacturing facility or sold to the grid.
Other objects and advantages will be more fully apparent from the ensuing disclosure and appended claims.